Posted by Ash from IP 220.127.116.11 on October 12, 2006 at 17:50:13:
6 steps to ABG analysis, go step by step in the very same order:-
1.Chk whether the pt is academic or alkalemic,by looking at the arterial pH (NL = 7.38 – 7.42)
2. Chk whether the ABG abnormality is due to a primary repiratory or metabolic disorder by chking the PCo2 levels( NL 38-42) and HCO3 levels (NL 22-26)
3. Now if there is respiratory component identified,chk whether this is acute or chronic respiratory acidosis or alkalosis.
4. Now if u identify a metabolic component ,chk whether it is high anion or normal anion gap M.Acidosis
5. Chk wether the respiratory system is adequetly compensating for this primary metabolic disorder.
6. Now u identify a high anion gap M.A,chk the corrected HCO3 level,y we do this coz to know wether there was a intial primary disorder ,before this new metabolic disorder developed.
VERY IMPO FORMULAS :- U have to learn the formulas byheart)
In Metabolic acidosis pH and HCO3 (DECREASES)
So to compensate for every 1 mmol/l of drop in HCO3 , 1.2mmhg of PCO2 shld decrease
In M.alkalosis pH and HCO3 (INCREASES)
So to compensate for every 1 mmol/l of increase HCO3, 0.07 mmhg of pco2 will increase.
In Resp .Acidosis (PH - DECREASED and PCO2 AND HCO3 INCREASED)
Acute R.acidosis:- For every 10 mmhg increase in pco2 , 1 mmol/l Hco3 shld increase
Chronic R acidosis:- for every 10 mmhg increase in pco2, Hco3 increases by 3.5mmol/l
In Respiratory Alkalosis pH INCREASED, pco2 and Hco3 DECREASED
Acute R.alkalosis :- for every 10 mmhg decrease in PCO2 , hco2 decreases by 2meq/l
Chronic :- for very 10 mmhg decrease in PCO2 ,hco3 decreases by 10mmol/l
Winters equation :- this equation helps u to determine ,what the expected PCO2 lloks like when there is a metabolic acidosis:-
( 1.5 x serum Hco3) + (8 +/- 2)
Anion GAP :- done always when the disorder is metabolic acidosis
NA - ( CL + HCO3) NL = 10- 12
The equation for Corrected bicarbonate:- measured HCO3+ (aniongap – 12)
Delta gap :- observed anion gap + normal anion gap = ANS + measured Hco3
Delta gap helps u know the anion gap was increased /normal before the development of new high anion gap.
CAUSES FOR HIGH ANION GAP M.A(‘HAGMA’)
methanol, ethanol, lactic acidosis, ketoacidosis, seizures, ethylene glycol,salicyclate poisioning(MA+ R.ALK),less commonly due to isoniazid and iron.
CAUSES FOR NORMAL ANION GAP M.A( ‘NAGMA’)
NG- tube,diarrhea,RTA,carbic anhydrase inhibitor.
After u master this formulas..i will post a new case on acid base disoder tomo morning,and go step by step as i mentioned above..and i am 100% sure u will get em all right
The source for all this are new england medical journals,ICU journals,and www.medscape.com
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